The present invention relates to an articulation arm for the variably positioned mounting in particular of office equipment, such as screens, telephones and the like, comprising a base part, which is to be fastened in a stationary manner, a bottom arm part, which is connected pivotably to the base part via a first articulation, and a top arm part, which is connected pivotably to the bottom arm part via a second articulation, it being the case that the top arm part is connected to the base part via a pull element which is guided over the articulations, and spring means are provided so as to produce a carrying force which supports the arm parts.
Such an articulation arm in the case of which, in order to compensate for different loading and lever lengths which depend on the respective spatial orientation of the articulation-arm parts, a pull cable is fixed in the base part, is guided over the first and second articulations and is fastened on the top arm part is known. Said pull cable is interrupted at one location, to be precise in the region of the bottom or of the top arm part, and is provided with a compensation spring here. In the case of said known articulation arm, the weight compensation is insufficient; at best, in the case of small loads, it is possible to achieve to a limited extent the situation where the arm parts remain static in any desired position.
The object of the present invention is thus to provide an articulation arm of the generic type in the case of which the weight compensation is improved such that, even in the case of loading with large loads, the arm parts are automatically retained statically in any desired position. Consequently, the articulation arm should also be suitable, in particular, for mounting heavy equipment, such as computer screens and the like.
This is achieved according to the invention in that the spring means have two spring elements, it being the case that a first spring element is arranged in the region of the bottom arm part, between the latter and the pull element, which runs continuously between the base part and the second articulation, and a second spring element is arranged in the region of the top arm part, between the latter and the pull element. This means that the first spring element is arranged in parallel with the pull element, while the second spring element is arranged in series with the pull element.
This configuration according to the invention first of all achieves the situation where it is possible to ensure a relatively high carrying force F as the sum of the individual forces F1+F2 of the two spring elements, it being possible for the spring elements, on account of the division, advantageously to be designed with a small and compact three-dimensional shape. This is advantageous, in particular, if the arm parts are designed as tubular, elongate hollow bodies and the spring elements are to be accommodated, together with the pull element, within the arm parts. This is because, in contrast to the spring division according to the invention, an individual spring element designed for a high carrying force would be of such a magnitude, in spatial terms, that interior accommodation would not be possible.
The invention also advantageously results in the two spring elements being connected in a force-fitting manner via the pull element, beyond the second articulation, such thatxe2x80x94depending on the movement of the top and/or bottom arm partxe2x80x94they act individually or together. The important factor here in each case is the movement of the arm parts relative to the stationary base part, i.e. the respective alignment in space (alignment relative to the horizontal and vertical). In this respect, each arm part is specifically assigned one of the two spring elements. If, for example, the two arms are pivoted together in space, then the two spring elements act such that their prestressing force changes. With just one of the two arm parts pivoting, it is only the prestressing force of the associated spring element which changes. For example, only the bottom arm part can be pivoted, as a result of which the top arm part is merely shifted parallel in space. In this case, there is only a change in the prestressing force of the first spring element, which is assigned to the bottom arm part. The same applies when it is only the top arm part which is pivoted. The invention makes it possible for spring elements to be coordinated very precisely with the respective weight and leverage ratios of the two arm parts.
In an advantageous configuration of the invention, it is also possible using specific compensation means, which are explained in more detail hereinbelow, for an automatic, very precise compensation of the respectively effective, horizontally measured lever-arm lengths, which change during the pivot movements, to be achieved such thatxe2x80x94in relation to each arm partxe2x80x94the carrying force produced by the respective spring element is always changed in dependence on the respective effective lever-arm length such that the articulation arm remains static in any desired position. Furthermore, it is even possible to achieve the situation where, even when the top arm part is pivoted out of an upwardly sloping spatial position, beyond the horizontal position, into a downwardly sloping position, the reshortening of the effective lever arm which occurs as a result is taken into account to the effect that, instead of a further increase in the carrying force, the force is increased to a less pronounced extent (degressively) or even is reduced again in accordance with the shortening effective lever arm.
In specific terms, this may advantageously be achieved in that the pull element is formed in two parts from a bottom pull part and a top pull part, it being the case that the two pull parts are connected in the region of the second articulation via a preferably disk-like deflecting element which can be rotated freely about the articulation axis. In this case, at least the top pull part is formed by a flexible pull cable which is fastened, on one side, on the deflecting element eccentrically to the articulation axis of the second articulation and, on the other side, on the top arm part indirectly via the second spring element. In order to vary the prestressing force of the second (top) spring element, the pull cable is guided, in the region of the second articulation, over a deflecting curve of the deflecting element. During the pivot movements, said deflecting curve has the pull cable wrapping around it to a more or less pronounced extent, as a result of which the prestressing force of the spring element is varied. According to the invention, it is thus possible, by a specific course of the radius of curvature, which may be designed to be constant or changing over the cable-deflecting path, to compensate for the change in the effective lever-arm length. The course of the deflecting curve may specifically be in the form of a section of a circle or helix.
The bottom pull part is also preferably designed as a pull cable and guided over a further deflecting curve of the freely rotatable deflecting element. It is advantageous here that the two deflecting curves may be designed in the same way or, in particular, differently. Thus, different radii of curvature which are constant or changing over the wrap-around path make it possible to realize virtually any desired kinematic step-up or step-down ratios, to be precise constant but also variable ratios (progressive/degressive).
Further advantageous configuration features of the invention can be gathered from the subclaims and from the following description.